Method and apparatus for inspecting sheets



G H. RENDEL.

METHOD AND APPARATUS FOR INSPECTING SHEETS Nov. 23, 1954 m4 m e a e m Filed March 18, 1952 United States Patent METHOD AND APPARATUS FOR INSPECTING SHEETS George H. Rendel, Pittsburgh, Pa., assignor to United States Steel Corporation, a corporation of New Jersey Application March 18, 1952, Serial No. 277,319

9 Claims. (Cl. 209-75) This invention relates to a method and apparatus for inspecting sheets, particularly sheets of tin plate. It is common practice to inspect tin plate for pin holes which are small perforations passing through the sheets. This is done by passing sheets between a highly concentrated light source and a photoelectric detector. -When material containing a perforation passes through the detector, light is transmitted through the perforation onto the photoelectric detector causing an electrical impulse. I have found that; these perforations are often angular and occasionally conical and that many holes are more plainly visible and more easily detected when viewed from one side of the sheet than when viewed from the other side. When inspecting sheets it is necessary to desensitize the hole detector circuits when there is no sheet in the detector and restore the sensitivity when a sheet is passing therethrough. I have found that it requires a slightly longer period of time to restore sensitivity to the hole detector than it does to desensitize it so that there is a greater length on the front end of each sheet than on the trailing end that will pass through the detector while it is desensitized.

It is therefore an object of my invention to provide a method of inspecting sheets in which the sheets are passed through two pin hole detectors in alternate directions of travel and inspected from opposite sides, thus providing for more efiicient inspection of a greater area of the sheets.

It is also an object of my invention to provide apparatus suitable for carrying out my improved method.

Another object is to provide apparatus for turning sheets end to end and upside down.

These and other objects will be more apparent after referring t the followin specification and attached drawing, in which the single figure is a schematic view of the inspection line.

Referring more particularly to the drawing. the reference numeral 2 indicates a piler for sheets S to be inspected. The sheets may be removed one by one from the piler 2 either manuallv or by means of a sheet feeder 4 such as the well known Dexter feeder. A conveyor 6 is located adjacent the piler 2 and feeds the sheets to a second conveyor 8. A pin hole detector comprising a light source 10 and ph tocell 12 is located between the convevors 6 and 8. The photocell 12 operates a control 14 which when energized will raise a deflector 16 at the end of conveyor 8 so as to direct the erforated sheet into the pile 18. A pin hole detector suitable for this purpose is shown in the copending application to Coleman and Rendel, Serial No. 272,471, filed February 19, 1952, entitled Sheet Pin Hole Detector. As the sheet passes over the conveyor 8 it passes through a thickness gauge 20 which is connected to operate a control 22. Sheets which are oif weight but are not perforated will pass over the deflector 16, a conveyor 24, and will be deflected downwardly into an off weight piler 26 by means of a deflector 28 which is operated by the control 22. Apparatus suitable for this process is disclosed in my copending application entitled Method and Apparatus for Gauging and Classifying Sheets and the Like, Serial No. 254,418, filed November 1, 1951. Sheets which are not off weight and in which no perforations have been found will pass over the deflector 28 to a conveyor 30 and hence to sheet re-.

versing apparatus 32. Apparatus 32 consists of spaced apart pulleys 34 and 36 around which passes an endless belt 38. One of the pulleys is driven by any suitable 2,695,098 Pa ented N v- 23, 1954 ice power means to rotate the belt 38. Magnets 40 are provided beneath the belt on its upper run to hold sheets S tightly against the belt. Electromagnets 42 are provided for holding sheets against the lower run of the belt. An endless belt 44 surrounds the belt 38 over a substantial part of its arc of contact with the pulley 36. The belt 44 passes around pulleys 46, 38 and 50. A photocell or trigger actuated switch 52 is provided adjacent the magnets 42 and actuates a control 54 for de-energizing the magnets '42 in the proper sequence to permit the sheet S to drop onto a conveyor 56 located beneath the magnets 42. Conveyors 58, 60 and 62 are arranged in tandem adjacent the conveyor 56. A light source 64 is provided between the conveyors 56 and 58 and a photocell 66 is located thercabove for actuating a control 68 similar to control 14. The control 68 operates a deflector 70 between the conveyor 58 and 60 to deflect sheets downwardly into a perforated sheet piler 72. A deflector 74 is located between the conveyor 60 and 62 and is actuated by a control 76 to deflect sheets downwardly into a pile 78. A prime sheet piler 80 is located at the end of conveyor 62. Y I

The operation of the device is asfollows: Sheets S are fed from the pile 2 and pass successively over the cone veyors 6 and 8. If a pin hole is detected in one of these sheets it is deflected downwardly into the pile 18. If a pin hole is not detected in the sheet but if it is off gauge as determined by the gauge 20 the deflector 28 will rise to deflect the sheet into the oil? weight pile 26. If no pin hole is detected and the sheet is the correct weight it will pass to the reversing apparatus 32 and Will be carried by the belt 38 around the pulley 36 where it is held in close engagement with the belt 38 by means of the belt 44. As the sheet emerges from the pass formed by the belts 38 and 44 it will be held in close engagement with the belt 38 by means of the magnets 42. When the front end of the sheet S reaches the switch 52 the magnets 42 will be deenergized, thus permitting the sheet to drop onto the conveyor 56. It will be seen that the mechanism 32 has turned the sheet end to end and upside down. The sheet S then passes under the photocell 66 and if a pin hole is detected therein the control 68 will cause the deflector 70 to rise, thus diverting the sheet to the piler 72. An operator standing adjacent the apparatus 32 will be able to inspect one side of the sheet as it passes over conveyor 30 or belt 38 and the other side as it passes over conveyor 56. When he sees any defect on the surface of the sheet he will operate the control 76 to cause the deflector 74 to direct the sheet into the deflect pile 78. All other sheets will pass into the prime piler 80.

While one embodiment of my invention has been shown and described it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

I claim:

1. The method of inspecting elongated sheets comprising passing sheets past a pin hole detector to detect pin holes therein from one side thereof, said sheets having a greater length on their front end than on their trailing end that will not be inspected by the detector, directing sheets with pin holes therein to a reject piler, turning the sheets end to end, then passing the sheets past a pin hole detector to detect pin holes therein from the opposite side thereof, and directing sheets with pin holes therein to a reject piler.

2. The method of inspecting elongated sheets comprising passing sheets past a pin hole detector to detect pin holes therein from one side thereof, said sheets having a greater length on their front end than on their trailing end that Will not be inspected by the detector, directing sheets with pin holes therein to a reject piler, gauging the thickness of said sheets, directing off gauge sheets to an off gauge piler, turning the sheets end to end, then passing the sheets past a pin hole detector to detect pin holes therein from the opposite side thereof, and directing sheets with pin holes therein to a reject piler.

3. The method of inspecting elongated sheets comprising passing sheets past a pin hole detector to detect pin holes therein from one side thereof, said sheets having a greater length on their front end than on their trailing end that will not be inspected by the detector, directing sheets with pin holes therein to a reject piler, turning the sheets end to end and upside down, then passing the sheets past a pin hole detector to detect pin holes therein from the opposite side thereof, directing sheets with pin holes therein to a reject piler, inspecting both sides of said sheets for surface defects, and directing sheets with defects therein to a reject piler.

4. The method of inspecting elongated sheets comprising passing sheets past a pin hole detector to detect pin holes therein from one side thereof, said sheets having a greater length on their front end than on their trailing end that will not be inspected by the detector, directing sheets with pin holes therein to a reject piler, gauging the thickness of said sheets, directing off gauge sheets to an ofi gauge piler, turning the sheets end to end and upside down, passing the turned sheets past a pin hole detector to detect pin holes therein from the opposite side thereof, directing sheets with pin holes therein to a reject piler, inspecting both sides of said sheets for surface defects, and directing sheets with defects therein to a reject piler.

5. Apparatus for inspecting elongated sheets comprising a group of conveyors over which the sheets pass, a pin hole detector adjacent the path of travel of said sheets, said sheets having a greater length on their front end than on their trailing end that will not be inspected by the detector, a deflector between two of said conveyors, a reject piler beneath said deflector, means operable by said pin hole detector to operate said deflector to direct sheets I with pin holes therein to said reject piler, a second group of conveyors over which the sheets pass, means between the two groups of conveyors for turning the sheets end to end, a second pin hole detector adjacent the path of travel of said sheets over said second group of conveyors, adeflector between two of said second group of conveyors, a reject piler beneath said second deflector, and means operable by said second pin hole detector to operate said second deflector to direct sheets with pin holes therein to said second reject piler.

6. Apparatus for inspecting elongated sheets according to claim including a thickness gauge for said sheets, a deflector between two of said conveyors, an off gauge piler beneath said last named deflector, and means operable by said gauge for operating said last named deflector to direct otf gauge sheets to said 01f gauge piler.

7. Apparatus for inspecting elongated sheets according to claim 5 in which the sheet turning means comprises a pair of spaced apartpulleys, a belt passing around said pulleys, means for rotating said belt, electro-magnetic means for holding sheets against the lower run of said belt, means for demagnetizing said electro-magnetic means, and a second belt surrounding said first belt over a substantial part of its arc of contact with one of said pulleys.

8. Apparatus for inspecting elongated sheets according to claim 7 including a thickness gauge for said sheets, a deflector between two of said conveyors, an off gauge piler beneath said last named deflector, and means operable by said gauge for operating said last named deflector to direct 011 gauge sheets to said off gauge piler.

9. Apparatus for turning elongated sheets end to end and upside down comprising a pair of spaced apart pulleys located in different vertical planes, a belt passing around said pulleys, means for rotating said belt, means for feeding sheets to the top run of said belt, electro-magnetic means for holding sheets against the lower run of said belt, means for demagnetizing said electro-magnetic means to release said sheets, and a second belt surrounding said first belt over a substantial part of its arc of contact with the pulley toward which the upper run of said first belt moves.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,358,061 Davidson et al Nov. 9, 1920 1,385,000 Grifiing July 19, 1921 1,873,860 Balletti Aug. 23, 1932 2,063,485 Carris Dec. 8, 1936 2,070,339 Moore Feb. 9, 1937 2,312,357 Odquist Mar. 2, 1943 2,527,911 Buccicone Oct. 31, 1950 2,540,766 Stillwell et al. Feb. 6, 1951 2,570,288 Todd Oct. 9, 1951 FOREIGN PATENTS Number Country Date 468,692 Great Britain July 6, 1937 

